A thermostat is a closed loop feedback control device which has as its inputs a preset temperature value and a measured temperature which is to be controlled so as to approach in value the preset temperature. A thermostat can have its output connected to a fuel metering device in a heating plant, for example. In the typical thermostat, the difference between the measured temperature and the preset temperature is determined and a corrective signal is output to the heating plant which will have the effect of reducing that difference. For example, if the preset temperature is higher than the measured temperature, the thermostat will output a signal to the heating plant to increase the rate of fuel being supplied to the heating plant. The greater the difference between the preset temperature and the measured temperature, the stronger will be the signal sent by the thermostat to the heating plant to increase the rate of fuel being supplied. Once the heating plant has accomplished the desired increase in the measured temperature, the typical thermostat arives at a neutral zone state where no corrective signal is being sent to the heating plant. But the higher rate of fuel being supplied to the heating plant will result in the measured temperature increasing substantially above the preset temperature. This will cause the thermostat to pass through the neutral zone and enter into a state opposite to its previous state, wherein the measured temperature is greater than the preset temperature. The thermostat responds to this condition by outputting a signal to the heating plant to reduce the rate of fuel being supplied so that the measured temperature will decrease toward the preset temperature. The excessive cycling of the measured temperature about the value of the preset temperature is an undesireable feature of prior art thermostats, because overcoming the thermal inertia of the building or boiler whose temperature is to be controlled, by cyclic overheating and underheating, is very wasteful of fuel and thermally stresses the heating plant. There are other drawbacks to prior art thermostats, such as the use of mercury-wetted switches which requires that the thermostat can only be mounted in one position and which also poses the risk of explosion when used in flammable environments. Typical prior art thermostats are bulky devices which can be obtrusively unesthetic in home or office use.